In general, examples of known leaching operations for copper sulfide ores via hydrometallurgy include a leaching operation comprising performing an agitated batch reaction with the use of sulfuric acid or hydrochloric acid (tank leaching) and a leaching operation comprising forming an ore heap, supplying sulfuric acid or hydrochloric acid to the top of the ore heap, and recovering liquid dripping therefrom due to the force of gravity (heap leaching). In addition, a method of efficiently leaching copper with the use of bacteria such as iron-oxidizing bacteria and recovering copper (bioleaching) has been known. In the case of bioleaching, iron-oxidizing bacteria oxidize iron (II) ions in a leaching solution into iron (III) ions that serve as oxidants. Such iron (III) ions cause leaching of copper in the ore. In addition, a sulfur component contained in the ore is oxidized into sulfuric acid by sulfur-oxidizing bacteria. The thus obtained sulfuric acid also causes leaching of copper in the ore.
Hydrometallurgy of copper sulfide ore has been applied in practice with the use of a secondary copper sulfide ore containing chalcocite, covellite, or the like. However, in the case of chalcopyrite which most abundantly exists as a copper resource, the copper leaching rate is significantly slower than that in the case of a secondary copper sulfide ore. In such case, it is difficult to efficiently carry out copper leaching.
Hence, a variety of techniques for increasing the rate for leaching copper from a copper sulfide ore containing chalcopyrite as a main constituent have been suggested. For example, a method wherein leaching is carried out by adding activated carbon and iron to a leaching solution and maintaining the oxidation-reduction potential (Ag—AgCl reference electrode) at 350 to 450 mV (JP Patent Publication (Kokai) No. 2005-15864 A) has been reported. Alternatively, methods involving pressurization to an atmospheric pressure or more and heating to 100° C. or more for leaching have been reported (JP Patent Publication (Kokai) No. 2003-328050 A, JP Patent Publication (Kohyo) No. 2001-515145 A, and JP Patent Publication (Kokai) No. 10-317072 A (1998)). However, such leaching methods are problematic in terms of cost increase, although the methods are effective for the improvement of the leaching rate.
In addition to the above techniques, a technique comprising using silver to promote leaching of chalcopyrite has been reported as an example (U.S. Pat. No. 5,730,776). However, it has also been reported that silver inhibits the iron-oxidizing capacity of iron-oxidizing bacteria (De, G. C., et al., Hydrometallurgy, (the Netherlands), 1996, vol. 41, pp. 211-229). Therefore, it is difficult to employ a combination of leaching with the addition of silver and bioleaching. In order to solve the above problem, a copper sulfide ore leaching process using a leaching tank and a bacteria culture tank separately has been suggested (F. Carranza, et al., Hydrometallurgy, (the Netherlands), 1997, vol. 44, pp. 29-42). However, in view of cost and ease of operation, it is desired that leaching and bacterial culture be carried out in a single tank.
Further, it has been known that effects of the addition of an organic nitrogen source during culture of iron-oxidizing bacteria are not significant in terms of iron-oxidizing capacity, resulting in an increase of approximately 20% at maximum in terms of the capacity. In addition, it has been known that the addition of an organic nitrogen source in a certain amount or more causes inhibition of iron oxidization (OLLI H. TUOVINEN, et al., APPLIED AND ENVIRONMENTAL MICROBIOLOGY, (the U.S.), 1979, vol. 37, pp. 954-958).